The present invention relates to a leg protection device having an airbag for protecting occupant""s legs in a vehicle from a collision with an object such as an interior panel in front of a seat in the event of a vehicle collision, and particularly directed to a leg protection device having an airbag provided therein with a plurality of chambers.
In a conventional leg protection device having an airbag inflated in front of the vehicle occupant to receive the legs in the event of a vehicle collision so as to protect the vehicle occupant, a single chamber is normally formed inside the airbag without partition as disclosed in Japanese Utility Model Publication (KOKOKU) No. 47-24110, Japanese Patent Unexamined Publication No. 05-208646, Japanese Patent Unexamined Publication No. 05-208653, and Japanese Patent Unexamined Publication No.05-213144.
The occupant sitting on a vehicle seat may assume various sitting postures, for example, with knees apart and/or with legs extending sideways. The positions of the knees may be often spaced apart from a center of the seat. Therefore, the airbag of the leg protection device is preferably designed to rapidly spread in the vehicle lateral direction after start of inflation. In addition, in order to prevent the occupant""s legs from colliding with any vehicle members in front of the vehicle seat when the legs plunge into the inflated airbag, the airbag is desired to securely receive and stop the occupant""s legs.
In the conventional leg protection device having an airbag with a single chamber therein, since a dimension of the inflated airbag in a vehicle longitudinal direction (hereinafter, sometimes referred to as xe2x80x9ca thickness of an airbag) tends to be large, sufficient inflation of the airbag with a large thickness can receive the occupant""s legs effectively. However, if the airbag having the single chamber therein is designed to expand laterally as well, a volume of the inflated airbag becomes so large that a gas generator is required to have significantly large generating capacity.
It is an object of the present invention to provide a leg protection device for the vehicle occupant, in which the airbag can be rapidly and widely expanded along a device in front of the vehicle seat even with the gas generator having a small generating capacity.
It is another object of the present invention is to provide the leg protection device for the vehicle occupant that can sufficiently receive and stop the occupant""s legs even with the airbag having a smaller thickness when inflated.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A leg protection device for a vehicle occupant according to the present invention includes an airbag installed in a vehicle member in front of a vehicle seat and a gas generator for inflating the airbag. The leg protection device has a feature in that the airbag is provided with a first chamber into which gas from the gas generator is first introduced, and a second chamber into which the gas passing through the first chamber is introduced. The first chamber and the second chamber are arranged to extend along the vehicle member when the airbag is inflated.
In the leg protection device of the present invention, when the gas generator is actuated to spout out gas in the event of a vehicle collision, first the gas flows into the first chamber and successively flows from the first chamber to the second chamber, thereby inflating the first chamber and the second chamber. In this case, since the airbag is deployed to extend along the vehicle member in front of the vehicle seat, the projection of the airbag from the vehicle member in a longitudinal direction of the vehicle is small, whereby a wider area of the airbag protects the occupant""s legs. In the present invention, an inlet of the second chamber may be narrowed. Because of the narrowed inlet of the second chamber, the gas in the second chamber hardly flows back to the first chamber when the occupant""s leg plunges into the second chamber. Accordingly, the leg can be received and stopped effectively by the second chamber.
Since both of the first and second chambers are designed to be deployed to extend along the vehicle member in front of the vehicle seat, an area of the airbag facing the occupant is large upon inflation, thereby being able to receive the occupant""s legs regardless of the leg positions.
In the present invention, the airbag has a front panel arranged to face the occupant and a rear panel arranged to face the vehicle member. It is preferable that the inside of the airbag is divided into the first chamber and the second chamber by a linear joint portion connecting the front panel and the rear panel. According to this structure, the thickness of the airbag upon inflation is limited to be small, whereby the airbag can be rapidly inflated even with the gas generator having small generating capacity.
Further in the present invention, it is also preferable that the inside of the airbag is divided into the first chamber and the second chamber by a partition panel connecting the front panel and the rear panel.
According to this structure, the thickness and a configuration of the airbag upon inflation can be adjusted at higher degree of freedom by changing a size and shape of the partition panel (for example, the length of the partition panel in a direction of connecting the front panel and the rear panel). When compared to the case where the front panel and the rear panel are connected to each other directly by a linear joint, stresses, which is applied to portions connecting the front panel and the rear panel to the partition panel when the inner pressure of the airbag is increased, are dispersed entirely over the connected portion and the partition panel, so the stress can be limited to be smaller. Accordingly, material of relatively low strength can be used for the respective panels, and sewing yarns or adhesives of relatively low strength can be used for the connected portions, thereby reducing the cost.
In the present invention, the second chamber extends in such a way that the gas can enter through its inlet to flow straight therein, thereby facilitating the inflation of the second chamber. In this case, the second chamber may be provided at its inlet with a partition extending in a direction perpendicular to the longitudinal direction of the second chamber in order to narrow a width of the inlet, thereby securely preventing the gas from flowing back from the second chamber.
In the present invention, the airbag may be provided with a plurality of second chambers, and at least one of the second chambers has a different size from that of the other second chamber. According to this structure, the leg protection device can be designed according to a design of the vehicle, a profile of the instrument panel and a layout of the seat. For example, in the case of the second chamber to be inflated in a small space between the vehicle member and the legs, the leg protection device is designed such that the thickness of the second chamber is small upon inflation. In the case of the second chamber to be inflated in a large space between the vehicle member and the legs, the leg protection device is designed such that the thickness of the second chamber is large upon inflation.
In the present invention, at least a part of the first chamber may extend substantially in a vertical direction of the airbag, and a plurality of the second chambers may extend substantially in a lateral direction. According to this leg protection device, the gas is dispersed or supplied from the first chamber to a plurality of the second chambers, thereby uniformly inflating the second chambers. Since the second chambers extend in the lateral direction, the occupant""s legs can be securely received and stopped by the second chambers even when the occupant""s legs are spaced apart from a center of the vehicle seat.
In the present invention, the airbag may further include a third chamber into which the gas passing through the second chamber is introduced and the inlet of the third chamber may be narrowed. Because of the narrowed inlet of the third chamber, the gas in the third chamber hardly flows back to the second chamber when the occupant""s leg plunges into the third chamber. Accordingly, the leg can be received and stopped effectively by the third chamber. Also in this case, by designing the second and third chambers to extend substantially in the lateral direction, the occupant""s legs can be securely received by the airbag regardless of the leg positions.
In the present invention, a chamber to receive the knees of the occupant is designed to have a larger thickness than those of the other chambers upon inflation, thereby effectively absorbing an impact on the knees and the thigh joints.
To make the thickness of the chamber for receiving the occupant""s knees larger than those of the other chambers, the chamber deploying in front of the knees of the occupant is designed to have a larger thickness than that of the other chambers.
To make the thickness of the chamber for receiving the occupant""s knees larger than those of the other chambers in the leg protection device of the present invention in which at least a part of the first chamber extends substantially in the vertical direction of the airbag and a plurality of the second chambers extend substantially in the lateral direction, one of the second chambers is located at the top of the airbag and this uppermost second chamber has a larger thickness than those of the other chambers, and the uppermost second chamber is to be deployed in front of the knees of the vehicle occupant.